Genome-wide linkage in a large Dutch consanguineous family maps a locus for intracranial aneurysms to chromosome 2p13.

BACKGROUND AND PURPOSE: Familial occurrence of intracranial aneurysms suggests a genetic factor in the development of these aneurysms. In this study, we present the identification of a susceptibility locus for the development of intracranial aneurysms detected by a genome-wide linkage approach in a large consanguineous pedigree. METHODS: Patients with clinical signs and symptoms of intracranial aneurysms, confirmed by radiological, surgical, or postmortem investigations, were included in the study. Magnetic resonance angiography was used to detect asymptomatic aneurysms in relatives. RESULTS: Seven out of 20 siblings had an intracranial aneurysm. Genome-wide multipoint linkage analysis showed a significant logarithm of the odds score of 3.55. CONCLUSIONS: In a large consanguineous pedigree intracranial aneurysms are linked to chromosome 2p13 in a region between markers D2S2206 and D2S2977.

Anticipation in familial intracranial aneurysms in consecutive generations.

Intracranial aneurysms (IA) are the major cause of subarachnoid haemorrhages (SAH). A positive family history for SAH is reported in 5-10% of the patients. The mode of inheritance is not unambiguously established; both autosomal dominant and recessive modes have been reported. In sporadic as well as in familial SAH, approximately 60% of the SAH patients are female. Recently, anticipation has been described in familial SAH. Since up to 15% of the SAHs are not caused by an IA, we have analysed anticipation, sex ratio and mode of inheritance only in families with patients with a proven IA in two consecutive generations. A total of 10 families were studied in which at least two persons in consecutive generations were affected by SAH, a symptomatic IA (SIA) or a presymptomatic IA (PIA). We also analysed published data from families with a proven IA in two consecutive generations on age of SIA onset and sex ratios among affected family members (both SIA and PIA). The age of SIA onset in the parental generation (mean 55.5 years) differed significantly from the age of onset in their children (mean 32.4 years). In the parental generation 11 men and 37 women were affected (both SIA and PIA), in the consecutive generation these numbers were 28 men and 32 women. There is a significant difference in sex ratio of affected family members when the generations are compared (P<0.02). No family could be found in which three consecutive generations were affected by an IA (SIA or PIA).

Characteristics of small breast and/or ovarian cancer families with germline mutations in BRCA1 and BRCA2.

For families with a small number of cases of breast and/or ovarian cancer, limited data are available to predict the likelihood of genetic predisposition due to mutations in BRCA1 or BRCA2. In 104 families with three or more affected individuals (average 3.8) seeking counselling at family cancer clinics, mutation analysis was performed in the open reading frame of BRCA1 and BRCA2 by the protein truncation test and mutation-specific assays. In 31 of the 104 families tested, mutations were detected (30%). The majority of these mutations (25) occurred in BRCA1. Mutations were detected in 15 out of 25 families (60%) with both breast and ovarian cancer and in 16 out of 79 families (20%) with exclusively cases of breast cancer. Thus, an ovarian cancer case strongly predicted finding a mutation (P < 0.001). Within the group of small breast-cancer-only families, a bilateral breast cancer case or a unilateral breast cancer case diagnosed before age 40 independently predicted finding a BRCA1 or BRCA2 mutation (P = 0.005 and P = 0.02, respectively). Therefore, even small breast/ovarian cancer families with at least one case of ovarian cancer, bilateral breast cancer, or a case of breast cancer diagnosed before age 40, should be referred for mutation screening.

Glomus tumours and genomic imprinting: influence of inheritance along the paternal or maternal line.

Two new families with glomus tumours and two additions to earlier publications are presented. The pattern of inheritance is autosomal dominant. Familial glomus tumours are inherited almost exclusively via the paternal line, a finding inconsistent with autosomal dominant transmission. This can be explained by genomic imprinting. The maternally derived gene is inactivated during female oogenesis and can be reactivated only during spermatogenesis. Two different loci have been assigned, one to a 5 cM region of chromosome 11q13.1 and one to 11q22.3-q23.3. Genomic imprinting has already been found for the distal locus and here we demonstrate that the proximal locus is subject to genomic imprinting too. Genomic imprinting has considerable implications for genetic counselling in families with glomus tumours. In addition to this the sex ratio among affected offspring appears to be influenced by the paternal or maternal origin of the gene of the transmitting father.

Fine mapping of a putatively imprinted gene for familial non-chromaffin paragangliomas to chromosome 11q13.1: evidence for genetic heterogeneity.

Autosomal, dominantly inherited, non-chromaffin paragangliomas are tumors of the head and neck region occurring with a frequency of 1:30,000. Genomic imprinting probably influences the expression of the disorder, because tumor development is limited to individuals who have inherited the trait from their father. By linkage analysis and haplotyping of a single large family in which the pattern of inheritance is consistent with genomic imprinting, we have mapped the gene to a 5 cM region of chromosome 11q13.1 between D11S956 and PYGM. A maximum lod score of 7.62 at theta = 0.0 was obtained for D11S480. This interval does not overlap with a recently assigned locus for glomus tumors in other families: 11q22.3-q23.3. Furthermore, analysis of a second family showing the imprinting phenomenon resulted in the exclusion of the 5 cM area as the location of the disease gene, whereas an indication for linkage was obtained (Z = +2.65) with markers from the distal locus. These observations argue for the presence of two distinct imprinted genes for glomus tumors on 11q. A model for tumor initiation and progression is presented based on all available information.